Cheaper in hardware. You only need one adder. On Thu, Aug 4, 2011 at 6:13 PM, Page Jack <jack.page...@gmail.com> wrote:
> Hi Colby, > I don't understand why compute RSSI need an IIR filter? as I know the rssi > can be compute > like that: (sample[0]*sample[0]+...sample[i]*sample[i]) / (i+1) > > > Regards! > > > On Thu, Aug 4, 2011 at 2:44 PM, Colby Boyer <colby.bo...@gmail.com> wrote: > >> On Wed, Aug 3, 2011 at 6:30 PM, Page Jack <jack.page...@gmail.com> wrote: >> >>> the code below is in sdr_lib/rssi.v I don't understand especially this >>> line: rssi_int <= #1 rssi_int + abs_adc - rssi_int[25:10]; >>> >>> wire [11:0] abs_adc = adc[11] ? ~adc : adc; >>> >>> reg [25:0] rssi_int; >>> always @(posedge clock) >>> if(reset | ~enable) >>> rssi_int <= #1 26'd0; >>> else >>> rssi_int <= #1 rssi_int + abs_adc - rssi_int[25:10]; >>> >>> assign rssi = rssi_int[25:10]; >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> Discuss-gnuradio@gnu.org >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >> It appears to be a clever way to implement a single pole IIR filter. Josh? >> >> If you recall an IIR is defined as y[n] = (1-alpha) * y[n-1] + x[n] >> >> Since multiplier are expensive in hardware, lets use a multiples of two so >> you can bit shift, then add and subtract. :D In this case alpha is 2^-10 >> >> --Colby >> > >
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